Hi Experts,
We are seeking your conclusion on this query from customer about design application with LM2991, a negative LDO. They wanted it to convert -6.5Vin to -5.0Vout.
From Section 7.4.1 of the device datasheet:
Does it mean if designed with -5Vout, a minimum of -10Vin is required?
I have left my understanding below to the customer and this is my stand:
We have the same understanding with the Vin requirements of this device. When we treat this in positive convention (disregard the negative polarity), the input requirement should be 5V higher than the output up to 26V, to regulate the device up to 1A output.
We are seeing from device description that it has 600mV drop-out voltage (typical) when operating a 1A load current. This drop-out means that at 1A, Vout will be ~(-4.4V). I have this high regard that this device requires a minimum voltage differential of (5V) in order to operate this up to 1A at normal condition.
But, upon checking from Figure 12:
the device seems that it should work on their application ( Vin=-6, Vout=-5, @ 1A ). Which is contrary to the above assertions.
Can you help us verify this application notes? I am seeing from our E2E threads that they are designing the device lower than 5V differential voltage and some experts supported it.
For your guidance please.
Regards,
Archie A.
PS: I tried this design on Webench and their requirements shared seems functional.
